Previously known versions of manufactured permeable paving based on adherent granules have been substantially rigid and liable to crack and break. Known binding agents used in prior-art pavers include a sand-free mortar based on a Portland cement or a thermosetting resin such as a two-pot epoxy resin. A significant setting time adds to the cost of manufacture for each. Pavers made using either option are weak and prone to catastrophic failure involving brittle fracture. A permanently set glue is not easily compatible with field repair.
Large flat areas of concrete require special attention to drainage since concrete is impervious. Such footpaths affect growth of cultivated shrubs and trees which may have roots extending beneath the footpath. Roots, or the soil around roots, require air. Therefore a highly pervious version of concrete would be desirable, considering the inevitable tendency for pores to be blocked by detritus.
Pervious concrete can be made using impervious concrete pavers with pervious joints between them. A recent publication (Comment by R Gaimster, p 54, “Contractor” (New Zealand), September 2010) describes a surface of 80×170 mm impermeable pavers separated by 10 mm permeable joints each comprised of sized gravel fixed in place with a sand-free concrete mix. Although the joint itself has a permeability of around 15-25%, the joint area is only 6% of the total paved area.